We have obtained well-labeled monkey fetuses using intravenous injections of 3H thymidine (3HT) into the pregnant female on a known day of gestation. Retinal sections have been double-labeled for cell birthdate (3HT autoradiography) and cell markers (immunocytochemistry). Currently three series are being collected at Fd45, Fd55 and Fd72, with 4-5 fetuses in each series. This material will provide an invaluable resource for the analysis of retinal growth and for determining the sequence of cell generation and differentiation within subpopulations of retinal neurons. An analysis of double-labeled dopamine amacrine cells has shown that these large cells are born somewhere in the middle of the amacrine types. They are never heavily labeled for 3HT, which would show that they are the first to be generated; the first amacrine cells to be generated are large amacrines which contain the neurotransmitter GABA. However, dopamine amacrines are significantly more labeled than other amacrines, putting them in the middle of the cascade of amacrine generation.